The present invention relates to air-liquid fuel mixing devices, and, more particularly, to a device which mixes liquid fuel and air and provides a uniform combustible air-fuel mixture under all operating conditions to one or more burning areas, such as the cylinders of a gasoline internal combustion engine, where complete combustion of the air-fuel mixture occurs.
The present invention finds particular utility as a carburetor for gasoline internal combustion engines and, accordingly, this statement of background will be given in the context of the carburetor art. The design and operation of improved carburetors for gasoline internal combustion engines has been the subject of extensive research and development work, especially since the dramatic increase in the price of oil (with further increases expected) and the enactment of federal and state regulations concerning the emission by automobiles of pollutants into the atmosphere. For example, 40 C.F.R. 85.076-1 (July 1, 1974) has prescribed that exhaust emissions from 1976 model automobiles may not exceed 0.41 grams of hydrocarbon per vehicle mile, 3.4 grams of carbon monoxide per vehicle mile and 0.40 grams of oxides of nitrogen per vehicle mile. Later amendments to the code imposed less stringent standards.
Ongoing research and development has been aimed at improving the mixing between the liquid fuel and the intake air drawn through the carburetor and developing a uniform mix of air and liquid fuel over the full range of operating conditions of the engine. Several of such carburetor designs are illustrated and described in the Eversole et al U.S. Pat. No. 3,778,038. The carburetors of the Eversole et al patent include an elongated upper section that tapers down to a point of minimum diameter and a lower section that diverges outwardly from the point of minimum diameter. A longitudinally adjustable regulating member is mounted within the carburetor and forms with the upper section a so-called constricted zone. Fuel outlets spray fuel into the air stream at or just forward of the point of minimum diameter. The divergence angle of the lower section is kept quite small, viz., the cross-sectional area in the lower section increases with distance as would a cone having an apex angle of 6.degree. to 18.degree.. According to the patent, this permits the formation of two zones in the lower section, a supersonic zone where the velocity of the fuel-air mixture is increased to supersonic and a subsonic zone where the velocity of the air-gas mixture is decelerated to subsonic.
A principal disadvantage with the type carburetors shown in the Eversole et al patent is that the air speed through the carburetor must be carefully controlled in order to insure the development of sonic and supersonic velocities for the air-fuel mixture. The development of such velocities is critical to the development of combustible fuel-air mixtures. Thus, abrupt changes in engine acceleration can result in stalling because of reduced air speed or incomplete combustion with the attendant emission of pollutants into the atmosphere. In addition, this type carburetor is susceptible to icing, condensation and high manifold vacuum producing low volumetric efficiency and therefore reduced engine power.